The present invention relates to optical networks. More particularly, the present invention relates to an optical ring network architecture.
The use of optical networks can dramatically increase the amount of information, such as telephone, video and Internet information, that can be communicated between network users as compared to traditional networks. Such an optical network can, for example, connect a number of terminal stations through a number of parallel optical fibers. When a user at a first terminal station wants to transmit information to a user at a second terminal station, the information is transmitted through one of the optical fibers with a dedicated wavelength of light.
The user at the first terminal station may also want to simultaneously transmit information to a number of different users located at a number of different terminal stations. Moreover, users at a number of different terminal stations may want to transmit information to each other simultaneously. Creating a network that lets all users communicate with all other users simultaneously, however, tends to increase the number of optical fibers that must be used in the network. Unfortunately, each additional optical fiber that is used can be very expensive to install and maintain. In addition, some networks need to be fully xe2x80x9crestorable,xe2x80x9d meaning that each user can still communicate with each other user when any one of the optical fibers fail. This also tends to increase the number of optical fibers required in the network.
One way to reduce the number of optical fibers in a network is to use Wavelength Division Multiplexing (WDM). In a WDM network, a set of wavelengths, such as xcex1, xcex2 . . . xcexn, are used so that several communications can be simultaneously transmitted over a single optical fiber using different wavelengths. To increase the amount of information that can be transmitted over the network, and to reduce the cost of optical transmitters, receivers and routers, it is desirable to keep the number of different wavelengths used in the network as small as possible.
In addition, to avoid interference in the network a single wavelength should not be used to simultaneously transmit different information over the same optical fiber in the same direction. Moreover, it may be necessary to amplify one or more signals being transmitted over an optical fiber in the network. In this case, it is desirable that information is not simultaneously transmitted over the same optical fiber using the same wavelength, even if the transmissions are in opposite directions.
In view of the foregoing, it can be appreciated that a substantial need exists for an optical network architecture that reduces the number of optical fibers and wavelengths used in the network and solves the other problems discussed above.
The disadvantages of the art are alleviated to a great extent by an optical ring network architecture including a number (N) of multi-add/drop filters, such as filters formed using symmetrical pairs of frequency routers. Each multi-add/drop filter is coupled to two other multi-add/drop filters using Nxe2x88x922 transmission media, such as optical fibers, to form a ring. The network also includes a number (N) of terminal stations associated with the multi-add/drop filters. A terminal station (p) is coupled with, and receives information from, its associated multi-add/drop filter (p) through a single optical fiber. In addition, the terminal station p is coupled with, and transmits information in a first direction around the ring to, a multi-add/drop filter p+1 through a single optical fiber.
Communications from terminal station p to each other terminal station in the first direction are assigned one of Nxe2x88x921 wavelengths such that no two wavelengths on a given optical fiber are associated with communications between terminal stations in the same direction. When there are four terminal stations, for example, the second terminal station may communicate with the first, third and fourth terminal stations using wavelengths xcex1, xcex3 and xcex2 respectively. Moreover, all wavelengths on a given optical fiber may be associated with a communication between terminal stations in either the first or second direction. As a result, each terminal station can communicate with each other terminal station simultaneously using wavelength division multiplexing and Nxe2x88x921 wavelengths. The network may also be bi-directional such that each terminal station p is coupled with, and transmits information in a second direction opposite the first direction to, a multi-add/drop filter pxe2x88x921 through a single optical fiber.